|Publication number||US7597948 B2|
|Application number||US 11/323,849|
|Publication date||Oct 6, 2009|
|Filing date||Dec 29, 2005|
|Priority date||Dec 29, 2005|
|Also published as||US20070175178, WO2007078946A2, WO2007078946A3|
|Publication number||11323849, 323849, US 7597948 B2, US 7597948B2, US-B2-7597948, US7597948 B2, US7597948B2|
|Inventors||Timothy Michael Miller|
|Original Assignee||Corning Incorporated|
|Export Citation||BiBTeX, EndNote, RefMan|
|Patent Citations (7), Referenced by (4), Classifications (24), Legal Events (3)|
|External Links: USPTO, USPTO Assignment, Espacenet|
This invention generally relates to ceramic honeycomb structures, and is specifically concerned with a honeycomb structure having reduced stress web-skin joints.
Ceramic honeycomb structures are known in the prior art. Such structures generally comprise a plurality of webs that define a plurality of cells, and a skin surrounding the plurality of webs and having an inner surface or inner wall integrally connected to peripheral ends of the webs. Such ceramic honeycomb structures are currently favored for use as ceramic catalyst substrates for automobile exhaust systems. To maximize contact between the exhaust and the catalyst coated over the webs, high cell densities on the order of 400-1200 cells per square inch are favored. However, to minimize the pressure drop with such a structure, thin webs on the order of 0.001 to 0.005 inches are typical. During manufacture, both the plurality of webs and the skin are simultaneously extruded such that sharp-cornered or filleted joints are formed between the peripheral ends of the webs, and the inner wall of the skin. The skin is typically made considerably thicker than the webs so that the extrusion which ultimately becomes the final ceramic honeycomb structure will have sufficient mechanical strength to endure the handling and cutting procedures required to render the raw extrusion into a final product.
Unfortunately, the sharp or slightly filleted interfaces between the thin webs forming the plurality of cells and the inner wall of the skin tend to concentrate mechanical stresses in these areas when mechanical forces are applied to the exterior of the skin during the manufacturing process. Additionally, the applicant has observed that the substantially greater thickness of the skin can create thermally-induced stresses at these interfaces, as the greater thickness of the skin inherently gives it a different coefficient of thermal expansion (CTE) than the substantially thinner cell walls, even though both walls are formed from the same ceramic material. Finally, the inventor has observed that during the extrusion process, these same differences in thickness between the webs and the skin creates differences in flow rate of the plasticized ceramic material as it is squeezed through the extrusion die that forms the honeycomb structure. It is theorized that these differences in the velocity of material flow weakens the joints between the peripheries of the outer webs and the inner wall of the skins.
Previous approaches to solving structural problems relating to honeycomb strength and/or the web-skin interface include a thickening of the webs in the vicinity of the periphery of the body (as shown in U.S. Pat. No. 4,233,351) and a heavier rounding or filleting of the corners of the joints between these components of the structure (as shown in U.S. Pat. No. 5,952,079 and U.S. Pat. No. 6,060,148). However, the thickening of the webs interferes with gas flow around the periphery of the structure, and the rounding of the corners of the joints does nothing to reduce stresses arising during the forming of the webs and skins which are thought to contribute to structural defects in the manufactured articles. Thus problems such as skin flaking and chipping from the outside of the fired honeycombs during handling, or even localized separations of the skin from the plurality of webs occurring during drying or firing, continue to be observed in some honeycomb designs.
Clearly, what is needed is a ceramic honeycomb structure having improved joints between the webs, and the skin which more effectively resists skin flaking and chipping, skin separation, and thermal damage in use. Such improved joints should not result in a significant thickening of either the webs or the skin such that larger thermally-induced stresses between these components would be created due to differences in CTE. Ideally, such joints would allow the skin to be made thinner so that the CTE differentials between the skin and webs could be reduced. Finally, it would be desirable if such stress-reduced joints could be easily produced by way of conventional extrusion techniques which would reduce or eliminate any differences in flow speed in the ceramic material in the joint interface area such that the resulting joints would be stronger.
Generally speaking, the invention is a ceramic honeycomb structure that fulfills all of the aforementioned criteria. To this end, the honeycomb structure comprises a plurality of webs that define a plurality of cells, a skin surrounding the plurality of webs and having an inner wall connected to peripheral ends of the webs such that a plurality of angularly spaced wall joints are formed around the inner wall, wherein portions of the inner wall disposed between the angularly spaced wall joints include continuous arches. Each of the arches includes a curved central portion that terminates in curved corner portions that are more sharply curved than the central portion. The continuous arches reduce stress in the interface between the peripheral ends of the webs and the inner wall of the skin by eliminating sharp corners or other angular interfaces between these components, and further by providing continuous support of the skin between the angularly spaced wall joints by providing an arch shape structure therebetween.
The curved central portion of the arch may be defined by a radius R2 and the curved corner portions may be defined by a radius R1 the radius R2 of the curved central portion of the arch may be as small as one-half of the width w of the cells, or as great as the radius R3 that defines the curved inner wall of the skin.
In a specific embodiment, wherein the cells have substantially uniform widths w, the skin is substantially circular and has a diameter D and a thickness ts, and the webs have a substantially uniform thickness tw, R2 ranges between the limits defined by
Additionally, the radius R1 of the corner portion ranges between the limits defined by
wherein 0.001 is inches.
The provision of continuous arches with rounded corner portions between the angularly spaced joints not only advantageously reduces stress in the interfaces defined by the joints, but further allows the skin to be made thinner relative to the webs, thereby advantageously reducing differences in the CTE between the webs and skin. Finally, such arches are easily produced via conventional extrusion techniques, and promote a more uniform flow rate of ceramic material through the extrusion tool, thereby reducing variations in the flow speed between the webs and the skin which applicant believes contributes to weakened joints between these two components and the final product.
With reference now to
A skin 9 is provided around the cell array 3 in order to give the structure 1 sufficient mechanical strength to withstand the various steps of manufacture without damage to the thin webs 7. Consequently, the skin 9 is typically formed on the order of about three times the thickness of the webs 7, and the peripheral ends 13 of the webs 7 are joined to the inner wall surface 11 of the skin 9 by way of integral joints 15, best seen in
Relatively sharp corners 17 are formed at the intersections of the webs 78, and the inner wall 11 of the skin 9. Such sharp corners tend to concentrate mechanical stresses created by differences in properties and/or temperatures of use between the peripheral ends 13 of the webs 17, and the relatively thicker skin 9. These stresses can arise in the course of honeycomb use, or earlier during honeycomb manufacture when the extruded, green bodies that ultimately form the honeycombs 1 are fired in a ceramic kiln in order to form the final ceramic structures. Even though the skin 9 and webs 7 will comprise the same material (typically cordierite) after firing, differences in thermal or physical properties between the webs and skins can give rise to stresses that, in the presence of micro-cracks or otherwise, can cause portions of the skin 9 to separate from or easily flake away from the fired honeycomb structure, rendering it useless.
In an attempt to solve this problem, the prior art has provided enlarged fillets in the joints 15 between the peripheral ends of the webs 13 and the inner wall 11 of the skin 9 to strengthen the interface between the webs 7 and inner wall 11. In
The arch 21 should be designed to maximize the contact area at the joints 15 while providing continuous support of the skin 9. In one embodiment, the curved central portion 22 is arcuate, although other curves (i.e., sections of ellipses, ovals, etc.) are also possible. In all cases, the curved central portion 22 should be designed to minimize the concentrated mass section which will affect the thermal responses of the skin 9 relative to the peripheral ends 13 of the webs. When the central portion 22 is arcuate, its radius R2 can be as small as half the width w of a cell 5 and as large as the radius of the inner wall 11 of skin 9. Accordingly, in a cylindrical, ceramic honeycomb structure 20 having a diameter D of 4.055 inches, a cell width or pitch w of 0.084 inches and webs 7 that are 0.004 inches thick and a skin 9 which is 0.01 inches thick, the range of the radius of an arcuate curved central portion 22 will be between 0.042 inches and 2.0175 inches. The curved corner portions 24 a, 24 b are also arcuate. In this example, the radius R1 is 0.005 inches. However, R1 may be as small as 0.0001 inches and as large as half the width or pitch w of the cell 7 (i.e., 0.084 inches). The following equations provide the design range of each of the radii R1 and R2:
While the invention has been described above with respect to specific illustrative embodiments, it will be apparent to those familiar with the art that numerous additions, variations and modifications of such embodiments may adopted for the practice of the invention within the scope of the appended claims.
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|Citing Patent||Filing date||Publication date||Applicant||Title|
|US9475245 *||May 8, 2012||Oct 25, 2016||Corning Incorporated||Honeycomb extrusion apparatus and methods|
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|US20110293882 *||May 27, 2010||Dec 1, 2011||Christopher Lane Kerr||Cordierite compositions for improved extrusion process quality|
|US20130300016 *||May 8, 2012||Nov 14, 2013||Thomas William Brew||Honeycomb Extrusion Apparatus and Methods|
|U.S. Classification||428/116, 428/192, 428/118, 428/304.4, 428/188, 428/134|
|Cooperative Classification||Y10T428/249953, B01D46/2474, Y10T428/24165, Y10T428/24149, B01D46/2466, B01D2046/2481, B01D2046/2496, Y10T428/24298, F01N2330/06, B01D46/2451, B01D2046/2492, B01D2046/2488, F01N2260/10, Y10T428/24744, Y10T428/24777, B01D46/2462, B01D46/247|
|Apr 7, 2006||AS||Assignment|
Owner name: CORNING INCORPORATED, NEW YORK
Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNOR:MILLER, TIMOTHY MICHAEL;REEL/FRAME:017772/0432
Effective date: 20060329
|Sep 28, 2010||CC||Certificate of correction|
|Mar 14, 2013||FPAY||Fee payment|
Year of fee payment: 4